21 8 TOWERS AND TANKS FOR WATER-WORKS. 



22,768Xi.4 I== 3 2 >i03 Ibs. For the tension in this connection 

 and allowing 10,000 Ibs. per square inch, the section area = 3. 2 

 inches. 



In smaller tower designs, the tie at the base of the tower is 

 frequently omitted, but in which case the horizontal thrust H of 

 the weight must be resisted by the direct shear on the anchor- 

 bolts and the friction of the shoe on the masonry pier. There 

 is then produced an overturning moment on the foundations 

 which must be provided for in foundation design, in order that 

 the resultant of the loads will come in the centre of the bearing 

 surface and avoid unequal settlement of the foundations. 



Bearing-plate. The thickness of the bearing-plate when 

 made of steel, with an allowable shear value of 12,000 Ibs. per 

 square inch to sustain safely the imposed load of 325,257 Ibs. 



92 C 2 ^7 



applied by a column section of 26.3 square-inch area, = ' * 



12.367 

 = = i square inch. 



12,000 



The other dimensions of the bearing-plate must be such as 

 to provide sufficient area to properly distribute the load over 

 the masonry foundation. 



A stone sill or cap is generally provided, surmounting the 

 pier and directly supporting the bearing-plate. The unit load 

 which it is considered good practice to allow upon a monolithic 

 capstone is taken at from 15 to 30 tons per square foot of bear- 

 ing, depending upon the character of the stone used. Assuming 



20 tons per square foot as a reasonable average, v =8 



40,000 



square feet, or \/i 152 = 34X34 inch plate required. 



Stability of Structure and Anchorage. Investigating the 

 stability of the structure upon the principle previously explained, 

 with the direction of the wind normal to the side of the square 

 formed by the tower frame, the tendency would be to overturn 

 about the base of the two leeward columns, and this must be 



